<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        body {
            padding: 20px;
        }
        
        div {
            height: 100px;
            width: 100px;
            background: green;
        }
        /* box-shadow 方案 */
        
        .case1 {
            box-shadow: 0 0 0 10px #655, 0 0 0 15px deeppink;
        }
        /* outline 方案 */
        
        .case2 {
            background: #655;
            border: 1px dashed #fff;
            border-radius: 30px;
            outline: 5px solid #655;
        }
    </style>
</head>

<body>
    <div class="case2"></div>
    <div>122</div>
</body>

</html>